I like the idea/theme that you've got going, but I'd like to make a few suggestions.
First, I'd increase the light levels. Personally, I'd do a daytime desert map (hot desert = lots of lighting). I like the large torches you've got outside of the monolith. I would definitely add some flames to the top. More light + detail = good!
I've also noticed that you're pretty much using two or three textures for the entire map. Try to vary the textures you use; there should be a bunch of different ones that will fit your theme.
I'd also recommend adding something like what's in this screenshot; something that will give your players a clear indication of who is controlling the point and where they should be headed towards. This should both act as a visual cue and project some more light both outside and inside of the monolith.
Next, we've got the interior of the monolith. You're faced with a few problems here. First, your point is somewhat cramped with relatively few access points. I could see demospam being a major problem here. You've also got too many torches sticking out of the walls. Even if they're clipped properly, it'll still make the space look smaller than it is. The lamps you've got in the corners are fine, though. The pillars surrounding the point are a nice thought, but why not replace them with something that completes the look of the map? Say, maybe, some translucent glass pillars that pulsate with energy the color of the controlling team?
I also like how you've got the drop-down access to the area. It'll let in some light from the exterior. May I suggest, however, adding a staircase in the area indicated? It'll take up some space, but it'll also add some vertical gameplay elements. I could see demomen and soldiers rocket and sticky-jumping onto the top of the monolith and spamming into that hole. The stairs (or a ramp) would allow other classes to remove them and continue defending the point.